1. Field of the Invention
The invention is related to the field of telecommunication services, and in particular, to a system that provides telephony services in a communications network.
2. Description of the Prior Art
Telecommunication regulations require carriers to enforce dialing rules. For example, the Federal Communication Commission mandates the number of digits dialed from a particular phone based on the numbering plan area (NPA) of an NPA-NXX-XXXX formatted phone number. Users in a particular NPA may be required to dial all 10-digits of an NPA-NXX-XXXX phone number. Users in another NPA might be required to dial only 7 digits.
In wireless networks, dialing rules are determined based on a device code provided from a device to the network during registration. A mobile station identifier (MSID) is an example of a device code, and a handset is an example of a device. When a user powers on a handset, the handset sends its MSID to a call processing system. A mobile switching center (MSC) is an example of a call processing system. An MSC uses the MSID to determine what dialing rules to enforce for calls placed from that handset. However, determining dialing rules based on the MSID has proven unreliable.
Directory codes from originating handsets could be used to determine dialing rules reliably. A phone number, or mobile directory number (MDN), is an example of a directory code. However, it is difficult for wireless carriers to obtain MDNs because handsets register with MSIDs, not MDNs. Additionally, carriers typically shield their customers' MDNs from other carriers.